Chemical Oceanography
Professor Ryan
Problem Set 1-2016
[email protected]
This problem set is designed to be open book and open notes, but you are expected to work
individually to obtain your answers. You should show all your work and clearly delineate how you
derived your results. This constitutes 10 % of your overall grade broken down as described on page 2.
You have 1.5 weeks to complete this assignment and submit it to me electronically in either MS Word
or Excel format (due 2/16/16 by 3:00 PM). Please name the file using the following system Lastname,
Firstname – PS1.(doc, docx, xls, or xlsx). I will confirm receipt of your assignment by return email.
Late submission will result in the loss of one point per day from the 10 point total. Please email me
concerning any specific questions so as not to use valuable class time on homework.
1)
Given the list below of the six major ions in seawater (SW) and the concentration of each
measured in an estuarine sample at 20 oC, prepare a table giving the concentrations in molarity (M),
molality (m) and molinity. Express your answers in scientific notation with the same number of
significant figures given for each species in the table. Use a density of 1.017154 kg L-1 for seawater.
Use the periodic table at the following link to obtain the needed atomic weight data
http://www.mbari.org/chemsensor/pteo.htm.
What 2 very obvious environmental factors affect the density of SW in this example and cause
it to be lower than what we have seen previously? (e.g. slide presented in class).
Concentration
Ion
Ca2+
mg L-1
(ppm)
mol L-1 (M)
(molarity)
mol kg-1 (m)
(molality)
mol kg-1
(molinity)
308.9
Mg2+ 963.0
Na+
8085
K+
299.3
SO 4 2- 2034
Cl-
14515
2)
Calculate the freezing point depression and boiling point elevation of a 0.7 m NaCl solution, a
0.7 m CaSO 4 solution and a 0.7 m CaCl 2 solution (i.e. pure water freezes at 0 oC, at what temperature
do these solutions freeze?). Use the equations and constants from class
ΔT f = - ν K f m
ΔT b = ν K b m
Normally the quantity “ν m“ would be 2 x molal concentration for NaCl or 3 x m for CaCl 2 . How
would you use the data for seawater in these equations if, for example, you had to do the calculation
for the sample in problem #1?
3)
Using data for the 6 most abundant ions in seawater (Table 3.5 from Emerson & Hedges),
calculate the ionic strength of seawater in moles/kg SW to the nearest 0.001. Compare this with the
ionic strength calculated in the same way (i.e., 6 most abundant ions in moles/kg) for Artificial
Seawater as described by Millero (2006) in Table 2.3 (see below). (Note: When selecting the 6
species, exclude carbonate, bicarbonate, fluoride and borate) What is different about carbonate,
bicarbonate, fluoride and borate compared to the other ions that might make us want to leave them out
of this calculation?
4)
Seawater contains both K+ and SO 4 2- which can react according to the following equilibrium to
form a singly charged soluble ion pair or complex
K+ + SO 4 2- <----> KSO 4 -
K f = 100.96 = 9.12
Using seawater total concentration data of 0.0104 M for K+ and 0.0289 M for SO 4 2, calculate
the concentrations of free K+, bound K (i.e., K in KSO 4 -), free SO 4 2- and bound SO 4 as well as the
percentage of each (i.e., free and bound K as a percentage of total K and free and bound SO 4 as a
percentage of total SO 4 ). Do the calculation first without making any correction for ionic strength,
then recalculate all values at an ionic strength of 0.5 using the Davies Equation. You may assume the
only equilibrium operating in this system is the KSO 4 - equilibrium given.
5)
Using total concentration data from the paper by Motekaitis and Martell (Mar. Chem. 21 (1987)
101-106) for the 18 components given in their Table I (excluding Hg), calculate with MINEQL+ all
species formed in seawater at pH 8.1 and an ionic strength of 0.5 at 20 oC. Prepare a table of the same
form as their Table VII to summarize your results.
Point values: 1) = 1.5, 2) = 1.5,
3) = 2.0,
4) = 2.5,
5) = 2.5
Total points = 10.0